METHOD AND APPARATUS FOR ALIGNING A PHOTOMASK

摘要

Apparatus and method for accurately aligning a semiconductor wafer to a photomask, comprising a base and a frame for the apparatus. The base portion includes a chamber in which is mounted a piston which is restrained from lateral movement while permitting vertical reciprocation thereof. In the upper portion of the piston is a socket which supports a gimbal, the gimbal including a surface for receiving a wafer thereon. Mounted on the frame is a carriage which includes a mask clamp for positioning a mask in superimposed overlapping relation relative to the gimbal while clamping the mask to the frame. A source of fluid is connected to the socket so that the gimbal will float on a cushion, for example, of air. The piston is elevated by air pressure to cause the piston to raise beyond the point of contact of a wafer mounted on the gimbal with the mask. In response to the increase in fluid pressure which results from the contact of the wafer with the mask a sensor stops the air pressure to piston. Thereafter the piston is lowered a preset and predetermined amount to thereby space the wafer from the mask permitting adjustment of the base relative to the frame.